The present invention relates generally to transducer moving or feeding mechanisms in apparatuses for recording and reproducing of signals on and from rotary recording mediums. More particularly the invention relates to a mechanism for feeding in traverse movement a transducer for carrying out recording and reproducing signals on and from a rotary recording medium, the mechanism being capable of thus feeding the transducer in a highly accurate and positive driving power transmission state and, moreover, without shock or vibration.
In the prior art, an apparatus wherein a plurality of magnetic heads are intermittently advanced alternately over a rotating magnetic medium, such as a magnetic disc or a magnetic sheet, in the radial direction thereof, and a television signal is alternately recorded on and reproduced from concentric tracks on the medium at a rate of one field in one track has been known. Recording and reproducing apparatuses of this character are disclosed in the specifications of references such as, for example, U.S. Pat. Nos. 3,649,752, 3,681,525, and 3,749,827.
Heretofore, apparatuses for recording and reproducing magnetic discs of the type wherein a magnetic head is caused to move intermittently over a rotary magnetic disc thereby to record and reproduce video signals with concentric tracks have been reduced to practice. As a device for moving the head in an apparatus of this type for recording and reproducing magnetic discs, a device is proposed as disclosed in the specification of U.S. Pat. No. 3,749,827, in which an endless belt passed around a driving shaft driven by a stepping motor (pulse motor) and a driven shaft are moved intermittently, and a magnetic head mounted on the endless belt is caused to move in traverse movement over the magnetic disc.
This device, however, has been accompanied by difficulties such as permanent elongation in the endless belt as result of a long period of use and the occurrence of uneven elongation in the belt when the driving shaft and the driven shaft are not precisely parallel, whereby the magnetic head cannot be moved over the magnetic disc accurately and positively over specific tracks. A further problem accompanying this device is that the magnetic head cannot be moved with accurate pitch because of occurrences such as slippage between the belt and the shafts, variation in the difference between the tensions in the belt on the driving shaft side and on the driven shaft side, and stretching and shrinking of the belt due to variations in temperature.
Accordingly, in order to solve the above described problems, we have devised a moving mechanism so constituted that, instead of the head moving mechanism described above wherein a head and shafts are used, a rack is fixed to a moving base or carriage on which a magnetic head is fixedly mounted, and a pinion provided on the rotor shaft of a motor is adapted to mesh with this rack, whereby rotation of the pinion by the motor causes the rack, and therefore the head, to move. In a device of this mechanical arrangement, however, there are a number of problems such as low accuracy of movement position of the head due to backlash between the rack and the pinion and transmission to the head of shocks between the rack and the rotating pinion, whereby satisfactory head movement cannot be attained. These problems become particularly serious in the case of an apparatus for recording and reproducing magnetic discs of a system wherein the motor rotates intermittently, and the head is moved intermittently.
Accordingly, in order to solve these problems, we have developed and reduced to practice a transducer feeding mechanism in an apparatus for recording and reproducing a signal on and from a rotary recording medium as described in the specification of U.S. Pat. No. 4,143,409. This previously developed transducer feeding mechanism comprises a rotational motive power source having a rotary shaft and a pinion provided on the shaft, a rack meshed with said pinion and fed in translational movement by the rotation of the pinion, two guide bars extending parallelly in the direction of feeding of the transducer, a first feeding carriage on which the rack is mounted and which is guided by the first guide bar, biasing means provided on the first feeding carriage and functioning to contact the second guide bar in an elastic manner and to urge the first feeding carriage in a direction to cause the rack to mesh further with the pinion, a second feeding carriage on which the transducer is mounted, and which is guided by the second guide bar, a guide member mounted on the second feeding carriage and contacting in a rotationally displaceable manner the first guide bar, and engagement means functioning to place the first and second feeding carriages in contacting engagement in the feeding direction along the first and second guide bars and in a mutually displaceable state within a plane perpendicular to the feeding direction.
In this previously developed transducer feeding mechanism, the rack meshes with the pinion with substantially no backlash, whereby the head is accurately fed in intermittent movement. Further, transmission of unwanted shock in directions other than the moving direction from the first carriage to the second carriage is prevented, whereby the head can be fed accurately and positively.
However, as described above, this previously developed transducer feeding mechanism is so constituted that first and second feeding carriages are caused to move as they are guided by first and second guide bars. Consequently, unless the first and second guide bars are set parallelly in all of the three-dimensional directions of space, the relative positional relation between the first and second feeding carriage will change as the feeding proceeds. Accordingly, in the assembly of the feeding mechanism, the first and second guide bars must be so adjusted and set that they will be parallel with respect to all directions. This assembly and adjustment is troublesome, which has been a problem. Another problem has been the high cost due to the necessity of using two guide bars which are required to conform to strict specifications of linearity, surface finish precision, and other characteristics.